Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of pollutants. The pollutants may be composed of gaseous compounds, which may include nitrous oxides (NOx), unburn-hydrocarbon (UHC), and solid particulate matter (PM), which may include unburned carbon particulates called soot.
High environmental standards have increased the burden on engine manufacturers to reduce the amount of nitrogen oxides (NOx) and other pollutants (e.g., PM, UHC) that may be emitted from the engines. Manufacturers also have a commitment to their customers to produce powerful yet fuel efficient engines. However, in most situations, it tends to be difficult to reduce all pollutants without aftertreatment while meeting the customer's needs for power and fuel efficiency.
NOx emission levels may be affected by engine combustion temperatures, local oxygen concentration, and residence time. The principal source of NOx is the oxidation of atmospheric nitrogen. When the temperature inside combustion chambers exceeds 1300 degrees C., nitrogen may combine with oxygen to form oxides of nitrogen, or NOx. Some engines rely on methods such as exhaust gas recirculation (EGR), for example, to lower combustion chamber temperature and reduce NOx formation. These methods may be insufficient to meet the standards promulgated by government agencies limiting NOx emissions.
One method of decreasing NOx emissions is described in U.S. Pat. No. 6,253,545 to Makoto Suzuki (“the '545 patent”). The '545 patent discloses that carbon dioxide is capable of reducing NOx in the engine exhaust gas. The '545 patent also discloses a system and method of generating carbon dioxide and introducing the carbon dioxide into the engine system. The system disclosed in the '545 patent includes a combustion device, which is separate from the internal combustion engine. Fuel (the same fuel for combustion in the internal combustion engine) and fresh air are introduced into the combustion device and are combusted within the combustion device. The exhaust gas from the combustion device is then introduced into the internal combustion engine. Because the combustion within the combustion device is operated with a stoichiometric combustion. There is enough oxygen for conversion of all the fuel into completely oxidized products. Therefore, the exhaust gas from the combustion in the combustion device includes a high amount of carbon dioxide.
While the system of the '545 patent may result in some NOx reduction, the combustion device in the '545 patent is complex and relatively expensive. Moreover, similar to other conventional methods (e.g., exhaust gas recirculation —EGR), the concentration of the carbon dioxide is still limited in the exhaust gas exiting the combustion device. As a result, this methods is only to reduce NOx of diesel engine emissions. It is desirable to directly reduce diesel emissions (NOx, UHC, PM) at same time from the combustion chamber of diesel engines.
The present disclosure is directed to overcoming one or more of the problems or disadvantages in the prior art power systems.